Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

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Technical RequirementsGreen RoofHow does a Green Roof work?Green roofs reduce runoff volume and peak flow through severalmechanisms. When it rains, the green roof’s foliage, growthmedium, and root uptake zone retain a substantial portion of thestormwater that would otherwise flow from the roof to the stormdrain system. The retention volume depends on many factors,including rainfall amount, depth and composition of the growthmedium, and the type, diversity, and maturity of the vegetation.Some of the retained stormwater is released to the atmospherevia evaporation and transpiration (after uptake by plants). Theremainder slowly infiltrates through the growth medium to theroof underdrains and is discharged to the storm drain systemwith the volume and peak flow rate reduced.Green roofs are a proventechnology and have beenused/tested in Europe forover 40 years. They aregaining recognition in the USfor the environmental,economic, and social benefitsthey provide. There are nownumerous applications in theSan Francisco/San Jose BayArea of California.Green roofs improve runoff water quality through a variety of biological, physical, and chemicalprocesses within the plants and growth media. At the roof surface, airborne particulate matter(encompassing a range of organic and inorganic compounds) is intercepted and taken up by plant foliage.When it rains, stormwater (and associated air pollutants) is retained within and filtered through the growthmedia and root uptake zone. Contaminants sorb to clay and organic matter within the growth media.Further pollutant removal is achieved by bioremediation and phytoremediation, carried out by bacteriaand fungi present within the root systems. Pollutant removal increases as the vegetation and root systemsmature.Other Names: Ecoroof, green rooftop, nature roofs, vegetated roof coversPlanning and Siting Considerations• Involve the landscape architect, licensed structural engineer and mechanical engineer early in thedesign process with the project architect, since architectural roof style (pitch/slope,configuration), roof structural requirements, building heating/cooling needs, vegetation selection,and irrigation needs go hand in hand.• Proper design and management of drainage is essential. Inadequate drainage may result in moreload that the roof can sustain;plant mortality; and/ordegeneration of the growthmedium.• Choose plants suitable for thelocal climate and consideringdesired future irrigation. Checkwith the local permittingagency for recommended plantsand planting guides for greenroofs.• Consider designing the greenroof to serve as a greenspaceamenity accessible to buildingtenants and/or the generalpublic. This is particularlyimportant quality of life benefitin dense, downtown urban areaswhere space for parks andnatural areas is at a premium.Pedestrian Walkway on Stanford University Parking Garage Green roof, PaloAlto, CA. Design by Rana Creek Living Architecture.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsGR-2 May 2007
Runoff Reduction Control Measure Fact SheetGreen RoofDesign CriteriaTable GR-1 provides design criteria for green roofs; many parameters vary depending on the type ofgreen roof (intensive or extensive). A Design Data Summary Sheet for green roofs (Table GR-3) isprovided at the end of this fact sheet. Presently, the only widely-accepted, established standards for greenroof construction are the comprehensive FLL standards developed in Germany. An American StandardTesting Methods (ASTM) task group is developing new standards for green roof installation; this factsheet will be updated after the new standards are approved and published.Table GR-1. Green Roof Design CriteriaDesign Criteria Extensive Green Roof Intensive Green RoofDesign VolumeWQV, see Appendix D in this Design Manualfor design requirements for volume-basedcontrol measuresSameDesign Drawdowntime12 hours 12 hoursGrowth Media 2 Typical depth:
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Stormwater Quality Design Manualfor
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Stormwater Quality Design Manual wa
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Table of contentsOutdoor Work Areas
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Table of contentsSF-1.SF-2.SF-3.SF-
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Other Development Community Reviewe
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1 IntroductionPurposeThis Stormwate
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IntroductionIn July 2003, the permi
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IntroductionFor redevelopment proje
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Introduction• The Appendices prov
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2 An Integrated Approach toEffectiv
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Integrated ApproachIt is also helpf
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Integrated ApproachPut landscaping
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Integrated Approachfactors will be
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Chapter 3Figure 3-1. Process for Ad
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Chapter 3runoff reduction first (ev
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Chapter 3As the name implies (and a
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Chapter 3Step 9: Establish Long Ter
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Chapter 4Source Control Fact Sheets
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Source Control Measure Fact SheetSt
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Source Control Measure Fact SheetFu
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Technical RequirementsSand FilterSa
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Technical RequirementsVegetated Swa
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Glossaryexposure of construction ma
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GlossaryLow Impact Development (LID
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GlossaryRegional Stormwater Quality
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Appendix ASubmittal RequirementsThe
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Sacramento County Supplemental Appl
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Example Post Construction Stormwate
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Typically maintenance agreements an
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Example Maintenance Covenant(Sacram
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Device in accordance with the maint
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[attach]DECLARANT’S ACKNOWLEGEMEN
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Recorded at the request of:CITY OF
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9. The obligations herein undertake
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EXHIBIT B[Map/Illustration]
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City of FolsomThe City of Folsom ow
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Appendix D-1: Residential Sites: Ru
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Form D-1d: Alternative Driveway Des
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Form D-2a: Disconnected Pavement Wo
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Appendix D-3Runoff Reduction Credit
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These tables refer to runoff reduct
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Mature TreeShape Canopy (dia.) Heig
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Appendix D4LID Credits Background R
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unoff from the driveway by 60% whil
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The designer must determine how man
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Or the ASCE-WEF method (Sacramento)
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Table 3 - Multipliers Based on Rati
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Using the Effective Area Managed in
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SMRC, The Stormwater Manager’s Re
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Flow-based control measure design s
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4. Apply the Rational Formula to ca
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5. Enter the capture curve selected
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1.201.000.80STORAGE (in)0.600.4024-
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1.201.000.80STORAGE (in)0.600.4048
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Subject: VEGETATED SWALE EXAMPLEPLA
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PART II:Routing Excess Runoff throu
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4. Design the OutletThe outlet shou
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Exhibit 1Water Quality Orifice Outl
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3. Calculate Planter Surface Area A
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• Bottom slopes of 0.01 to 0.05%
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Appendix HDrainage Design and Storm
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